This invention relates to an improved flat communications cable. More particularly, it relates to a shielded flat communications cable having improved cross-talk and longitudinal balance.
In multi-pair communications cable, a principal concern is to maintain pair-to-pair cross-talk at acceptable levels so that transmissions on one pair do not interfere with transmissions on an adjacent or nearby pair. The problem of cross-talk in round cables is solved somewhat by twisting together the conductors of each pair so that the electric fields are, to a certain extent, cancelled. Some telephone cables, particularly the larger varieties, that is 25 pair and above, have used metal screens and shields in order to reduce the cross-talk. One example is shown in U.S. Pat. No. 3,622,683 assigned to the Superior Continental Corporation. The Superior patent shows a metal screen dividing a multi-pair cable core into two halves.
With the advent of flat cable and particularly with the advent of extruded jackets, the communications cable industry has been turning more and more to flat construction. Flat cable has advantages over round cable, particularly in the ease of gang termination to a connector and furthermore, the conductor pairs are maintained in a fixed space relationship for ease of identification. Flat cables also have a low profile so that they can be installed under carpets. One of the problems in flat cable construction for communications cable is the difficulty in controlling cross-talk. The twisted-pair approach is not acceptable because it raises the profile of the cable and it is difficult to maintain proper electrical characteristics. One attempt at this type construction is disclosed in U.S. Pat. No. 3,764,727 issued to Western Electric Company; however, this construction is very difficult to manufacture.
Manufacturers of flat telephone and data cable have also utilized metal shields on either side of the flat cable such as the shields 10 and 12 in the cable shown in FIG. 1. Other examples of similarly shielded flat cables are shown in the 1969 edition of the "Tape Cable, Flat Cable Bulletin".
Another type of shielded flat cable is shown in U.S. Pat. No. 3,459,879 issued to Gerpheide. The Gerpheide patent shows a multi-conductor flat cable having a metal shield sewn to the top part of the cable. Yet another shielded flat cable is shown in U.S. Pat. No. 3,576,723 issued to Angele. The Angele patent shows the shielding which is somewhat of a ridge and valley construction between each conductor.